Impotence or erectile insufficiency is a widespread disorder that is thought to affect about twelve percent of adult men under age forty-five, about twenty percent of men at age sixty, and about fifty-five percent of men at age seventy-five.
There is more than one cause of erectile dysfunction. For example, erectile dysfunction can be psychological, resulting from anxiety or depression, with no apparent somatic or organic impairment. Such erectile dysfunction, which is referred to as "psychogenic", is responsible for about fifteen to twenty percent of cases of impotence. In other cases, the erectile dysfunction is associated with atherosclerosis of the arteries supplying blood to the penis; such dysfunction is referred to as "arteriogenic" or "atherosclerotic." About forty to sixty percent of cases of impotence are arteriogenic in origin.
In still other cases, there is leakage from veins in the penis such that sufficient pressure for an erection can be neither obtained nor maintained. This dysfunction is referred to as "venous leakage," or "abnormal drainage". This condition is often exacerbated by the presence of some arteriogenic dysfunction whereby the supply of blood to the penis is impaired. In still other cases, the dysfunction is associated with a neuropathy, such as nerve damage arising from, for example, surgery or a pelvic injury, in the nervous system affecting the penis. Such a dysfunction is referred to as "neurogenic" and this accounts for about ten to fifteen percent of cases of impotence.
There is also a high incidence of erectile insufficiency among diabetics, particularly those with insulin-dependent diabetes mellitus. Erectile dysfunction in diabetics is often classified as "diabetogenic," although the underlying dysfunction is usually neurogenic associated with neuropathy, but may be arteriogenic or neurogenic and arteriogenic. About half of diabetic males suffer from erectile insufficiency, and about half of the cases of neurogenic impotence are in diabetics.
Additionally, erectile insufficiency is sometimes a side effect of certain drugs, such as beta-blockers that are administered to reduce blood pressure in persons suffering from hypertension, or drugs administered to treat depression or anxiety. Excessive alcohol consumption has also been linked to erectile insufficiency. These forms of erectile insufficiency may be regarded as a subset of neurogenic or psychogenic insufficiency.
A number of methods to treat impotence are available. These treatments include pharmacological treatments, surgery and, in cases of psychogenic dysfunction, psychological counseling is sometimes effective. Psychogenic impotence often can be cured by counseling coupled with a demonstration to the patient that he is capable of having a full erection by inducing such an erection once or a few times in the patients. Insufficiency due to excessive alcohol consumption is sometimes cured by reducing or elimination such consumption.
In rare cases, where the insufficiency is physical because of venous leakage, surgery can usually be employed to repair the venous lesion and thereby either cure the insufficiency or, if there remains an erectile insufficiency after repair of the venous lesion, render the insufficiency amenable to treatment by pharmacological methods. Also, penile implants, which provide a mechanical means to produce an erection sufficient for vaginal penetration, are widely used to treat impotence. In recent years, implants have been employed, especially in cases where pharmacological intervention is ineffective, which are usually cases of severe atherogenic impotence. Treatment of impotence with penile implants, however, entails serious disadvantages. Such treatment requires surgery and necessitates total destruction of the erectile tissues of the penis, forever precluding normal erection.
Pharmacological methods of treatment are also available. Such methods, however, have not proven to be highly satisfactory and can be accompanied by severe side-effects. Papaverine is now widely used to treat impotence, although papaverine is ineffective in overcoming impotence due, at least in part, to severe atherosclerosis. Papaverine is effective in cases where the dysfunction is psychogenic or neurogenic and severe atherosclerosis is not involved. Injection of papaverine, a smooth muscle relaxant, or phenoxybenzamine, a non-specific blocker and hypotensive, into a corpus cavemosum has been found to cause an erection sufficient for vaginal penetration. Also, in cases where severe atherosclerosis is not a cause of the dysfunction, intracavemosal injection of phentolamine, an .alpha.-adrenergic blocker, causes an erection sufficient for vaginal penetration. The resulting erection is one of significantly shorter duration than that induced by intracavernosal injection of papaverine or phenoxybenzanmine and is of such short duration that satisfactory sexual relations are difficult or impossible.
Treatment of impotence with papaverine or phenoxybenzamine often results in priapism, a locking-up of an erection for a long period of time, typically a few hours and sometimes longer than twenty-four hours. Priapism is a serious, deleterious side effect of treatment of erectile insufficiency with these drugs. Beyond the embarrassment that may be caused for some men, priapism is usually painful, irreversibly damages erectile tissue, and, to be relieved, requires bleeding or pharmacological intervention, such as injection of a sympathomimetic drug, such as adrenaline.
Even if priapism does not occur with use of papaverine, such use is associated with a painful, burning sensation in the first two or so minutes after the injection and there are indications that repeated use of papaverine causes undesirable, extensive intracavemous fibrosis. Further, as indicated above, impotence arising from severe atherosclerosis is not susceptible to treatment with papaverine, phenoxybenzamine, phentolamine or papaverine together with phentolamine. In any case, phenoxybenzamine is not suitable for use in treating impotence because it is a carcinogen.
Thus, although impotence is a ubiquitous problem, there are few satisfactory methods available for treating this disorder. Because of the relatively invasive intervention involved and the high failure rate of penile prostheses, surgical approaches provide unattractive alternatives. A safe pharmacological approach to the treatment of impotence is still to be achieved.
What is needed is a pharmaceutical that is effective but lacking in significant side effects.